Let's try for a few brief points here.
1. Cain's wife was his sister. Incest was not defined nor forbidden until the time of Moses. The first people created were genetically perfect and thus there was no problem with marriage to close relatives. In fact, historically, this was preferred. Abraham was married to his half-sister Sarah. They sent back to the family home to find a relative for their son, Isaac, to marry. When Esau, the eldest of Isaac's twins, married outside the family, it was a matter of great grief to his parents. His younger twin, Jacob, went back again to the family home and married his cousins. In Europe the idea of keeping a bloodline 'pure' in royalty ended up with the scourge of hemophilia in the males. In Hawaii the ancient royalty had to be a product of a brother/sister relationship, the brother and sister being the children of the current monarchs! However we find a prohibition against this close a marriage by the time of Moses in Hebrew culture. It would have been about this time that the genetic load in the human race would have built to a dangerous level. But at the time of Cain there was no danger at all.
2. No, no other people were newly created after Adam and Eve. However we do learn in Genesis 5 that, after Seth, Adam lived 800 years and had other sons and daughters. If Eve only had a baby every three years, there would have been no problem with her having at least a hundred children. In fact, a number of her grandchildren and great grandchildren could easily have been older than some of her children.
3. Thus, by the time Cain built the city, his own side of the extended family could easily have numbered between several hundred and a few thousand.
4. Actually, the world and universe are closer to 8000 than 6000 years old. The Masoretic text left out ciphers for '100' a number of times in the geneologies, for whatever reason.
5. Bones and fossils are showing atomic years in dates, and not orbital years. They are not the same thing, as shown by Tom van Flandern in 1984 in "U.S. Bureau of Standards special publication No. 617".
6. The Bible is not in error.
7. Marsupials, as well as all othre animals, migrated around the world before the separation of the continents, which happened several hundred years after the Flood at the time of Peleg.
8. The exploding waters of Genesis 7:11 were from the superheating of materials under the earth's crust. The heating was caused by radioactive decay, and the heat drove water out of the serpentine (much of the original earth material, which is over 10%water), turning it to olivine, and, when the critical point was reached, this super-heated water exploded out of the crust at the fracture zones which would later become the edges of the continental plates. A number of the ancient histories of old cultures recall these waters as scalding everything. Think Yellowstone exponentially.
9. God did not erase wickedness from the world (obviously!), but the Flood was timed to stop the wickedness and violence of the antediluvians. What the Flood did accomplish is indicated by the lifespans listed for those after the Flood. They dropped by half or more, immediately. Possibly this was because the Flood marked the first exposure of life on earth to the radioactive elements which had, up to that time, been buried beneath the crust (standard geology). This could have caused the mutations which led to the inability of cells to reproduce themselves as many times, thus limiting the life spans of man and probably a good many other critters.
10. God created nature and works through it. When He circumvents it, we call it a miracle, but the fact that He works through the laws He made for His own creation should not be a surprise.
11. The frozen mammoths are not a result of the Flood. Their deaths came probably as a result of an axis tilt of the earth which would have quickly frozen the northern regions. This axis tilt which also precipitated the ice age at the time of Job.
12. I didn't take the time to see the movie, but any idea that the scalding waters exploding from under the crust came back down as ice is ridiculous. Even if they exploded high enough to freeze, they would have been descending again through the scalding waters still exploding, and thus would have melted.
13. Again, the eras are aged due to radiometric dating, which is the result of atomic processes. These atomic processes have been measured as changing and thus we cannot connect them with orbital, or calendar years without some kind of formula.
14. It is inBREEDING, not inBREADING. God did not bake animals....
15. The original created populations of every kind of organism had perfect genetics, without any mutations present. Mutations mean changes and the original, by definition, has no changes. Mutations may well have been initiated primarily by the exposure to radioactive materials carried up with the pulverized rocks during the explosions of water which marked the Flood of Noah.
16. God did not have to put water beneath the crust miraculously. It was there in the rocks (olivine) and there is still enough of it there now to fill the oceans again.
17. Helix does a very good job of remembering what the BBC presents. He does not do a very good job of checking whether or not what they say is fact or supposition, however.
18. The water from the Flood drained into the current ocean basins.
19. The vapor canopy probably did not contribute a lot to the Flood, although the Flood probably did destroy a lot of it. It's primary purpose may well have been to shield us from UV radiation, and that new exposure after the Flood may also have had something to do with shortening life spans. There is some strange evidence to this day for the vapor canopy, but not nearly as low as our own clouds. It may well have existed in the upper regions of the atmosphere in an area called the thermosphere, which has alternating bands of extreme cold and extreme heat. There are still some water droplets which show up on photographs taken by spacecraft re-entering the atmosphere. Scientists did not know what to make of these strange 'specks and blobs' on the photos at first, but they are water. There may have been a lot more at one time....
20. Science has NOT shown that the world is billions of years old. Science has discovered that several billion ATOMIC years have passed. This is quite different from orbital years. In Genesis 1:14, the Lord tells us to count our time and seasons by orbital, or gravitational, years. These have remained constant. Many atomic processes, we have found, have not.
21. Actually, I agree with Helix that to attribute genetic defects DIRECTLY to sin is probably a mistake. We see consistent long ages of the antediluvians in Genesis 5. There may have been a few mutations before the Flood, but from what little evidence the Bible gives us, my guess would be that the stronger exposure to UV radiation (the destruction of at least part of the vapor canopy) and exposure to radioactive elements for the first time would have been the cause of the first major series of mutations in living organisms after the Flood.
22. While saying 'science and the Bible' agree or disagree may be popular, I would prefer saying the data and the Bible agree. Science may do strange things with the data, forcing it in a different direction, but when the actual raw data is examined, it supports exactly what the Bible tells us.
23. With all due respect to Walt Brown, who is a personal friend, we disagree with him on several issues regarding the 'problems' with the vapor canopy. It is very probably it was dispersed throughout the thermosphere, which is hundreds of miles thick.
24. Back to Adam and Eve -- perfect genes means no mutatons or defects. We have definitely come downhill from that point! And, if our teleomeres had the capacity via telomerase (which we can no longer produce) to reconstruct themselves, a thousand years of life would not be impossible for a human being. There are places on our genomes which are very sensitive to mutations, and if the ability to produce telomerase (which cancer cells can do!) were one of the things knocked out, there go our life spans down the drain post haste.
25. Adam was not fictional.
26. Aineo, be careful about saying never. Some women's names are found in genealogies. Check Matthew 1:5, for example....